Micro-light-emitting diode device

ABSTRACT

A micro-light-emitting diode device includes a first semiconductor layer, an active layer, and a second semiconductor layer. The first semiconductor layer has a first bottom surface. The active layer is disposed on the first semiconductor layer. The second semiconductor layer is disposed on the active layer. The second semiconductor layer and the active layer have an interface. A surface of the second semiconductor layer opposite to the active layer is a light-exiting surface of the micro-light-emitting diode device. A distance between the light-exiting surface and the interface decreases from a central axis of the second semiconductor layer to an edge of the second semiconductor layer, so as to provide a focusing effect for the light by the light-exiting surface.

RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 15/060,885, filed Mar. 4, 2016, which claimspriority from Taiwanese Application Serial Number 104115267, filed May13, 2015, which is herein incorporated by reference. All of theseapplications are incorporated herein by reference.

BACKGROUND Field of Disclosure

The present disclosure relates to a micro-light-emitting diode device.

Background of the Disclosure

With the progress of science and technology, light-emitting diodes havealready become common devices that are widely applied to commercialusages. As a light source, light-emitting diodes have plenty ofadvantages, which comprise low energy consumption, long service time,and fast switching. As a result, traditional light sources havegradually been replaced by the light-emitting diode light sources.

Apart from serving as a light source, light-emitting diode technologyhas been developed in the display field. For example, themicro-light-emitting diode display technology in whichmicro-light-emitting diodes (micro-LEDs) are formed to serve as pixelshas been developed in recent years.

However, as compared with a prior art light-emitting diode, amicro-light-emitting diode has a smaller light-emitting area. Since themicro-light-emitting diode has a smaller light-emitting area, itcontributes to the inadequate light extraction efficiency of themicro-light-emitting diode. In other words, micro-light-emitting diodeshave the problem of insufficient brightness.

SUMMARY

In one aspect of the present disclosure, a micro-light-emitting diodedevice is provided. In certain embodiments, the micro-light-emittingdiode device includes a first semiconductor layer, an active layer, anda second semiconductor layer. The first semiconductor layer has a firstbottom surface. The active layer is disposed on the first semiconductorlayer. The second semiconductor layer has a second bottom surface. Thesecond semiconductor layer is disposed on the active layer. A surface ofthe second semiconductor layer opposite to the active layer is alight-exiting surface of the micro-light-emitting diode device. Thesecond semiconductor layer has multiple thicknesses. A minimum thicknessof the second semiconductor layer is located at an edge or at least oneside of the second semiconductor layer. Vertical-projection zones of thefirst semiconductor layer, the active layer, and the secondsemiconductor layer on the first bottom surface are substantially thesame.

In one aspect of the present disclosure, a micro-light-emitting diodedevice is provided. In certain embodiments, the micro-light-emittingdiode device includes a first semiconductor layer, an active layer, anda second semiconductor layer. The first semiconductor layer has a firstbottom surface. The active layer is disposed on the first semiconductorlayer. The second semiconductor layer is disposed on the active layer.The second semiconductor layer and the active layer have an interface. Asurface of the second semiconductor layer opposite to the active layeris a light-exiting surface of the micro-light-emitting diode device. Adistance between the light-exiting surface and the interface decreasesfrom a central axis of the second semiconductor layer to an edge of thesecond semiconductor layer, so as to provide a focusing effect for thelight by the light-exiting surface. Vertical-projection zones of thefirst semiconductor layer, the active layer, and the secondsemiconductor layer on the first bottom surface are substantially thesame.

In some embodiments, the light-exiting surface of the secondsemiconductor layer has a first apex and a first end point. A verticaldistance between the first apex and the second bottom surface is amaximum among the thicknesses of the second semiconductor layer. Avertical distance between the first end point and the second bottomsurface is a minimum among the thicknesses of the second semiconductorlayer.

In some embodiments, a vertical distance between the light-exitingsurface of the second semiconductor layer and the second bottom surfacegradually decreases from the first apex to the first end point.

In some embodiments, the light-exiting surface of the secondsemiconductor layer is in a spherical shape, in an inverted-T shape, orin a pointed shape.

In some embodiments, the light-exiting surface of the secondsemiconductor layer has at least one microstructure. The microstructureincludes a plurality of recessed portions or a plurality of raisedportions.

In some embodiments, a shape of the first bottom surface of the firstsemiconductor layer is a circle or a polygon, and the shape and a sizeof the first bottom surface are substantially the same as a shape and asize of the second bottom surface.

In some embodiments, the vertical distance between the first apex andthe second bottom surface is more than 0 micrometer and less than orequal to 20 micrometers.

In some embodiments, the vertical distance between the first end pointand the second bottom surface is more than 0 micrometer and less than orequal to 10 micrometers.

In some embodiments, a difference between the vertical distance betweenthe first apex and the second bottom surface and the vertical distancebetween the first end point and the second bottom surface is more than 0micrometer and less than or equal to 10 micrometers.

In some embodiments, the second semiconductor layer has a firstthickness corresponding to a first area. The second semiconductor layerhas a second thickness corresponding to a second area. The firstthickness is greater than the second thickness such that the secondsemiconductor layer has at least one step between the first area and thesecond area.

In some embodiments, an area corresponding to the first thickness of thesecond semiconductor layer occupies 65% to 85% of a total area of thelight-exiting surface.

In some embodiments, the second area surrounds the first area.

In the foregoing, the micro-light-emitting diode device further includesan electrode layer disposed on the second semiconductor layer.

In summary, an embodiment of the present disclosure provides amicro-light-emitting diode device. The micro-light-emitting diode deviceincludes the second semiconductor layer. A surface of the secondsemiconductor layer is the light-exiting surface, and the secondsemiconductor layer has a greater thickness at the center than at theedge. Therefore, the cross section of the light-exiting surface has amore protruding center. As a result, the probability of the reflectedlight inside of the micro-light-emitting diode device by can beeffectively reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B respectively depict a three-dimensional schematicdiagram and a cross-sectional view of a micro-light-emitting diodedevice according to a first embodiment of this disclosure;

FIG. 2 depicts a cross-sectional view of a micro-light-emitting diodedevice according to a second embodiment of this disclosure;

FIG. 3A and FIG. 3B respectively depict a three-dimensional schematicdiagram and a cross-section view of a micro-light-emitting diode deviceaccording to a third embodiment of this disclosure;

FIG. 4A and FIG. 4B respectively depict a three-dimensional schematicdiagram and a cross-section view of a micro-light-emitting diode deviceaccording to a fourth embodiment of this disclosure;

FIG. 5A and FIG. 5B respectively depict a three-dimensional schematicdiagram and a cross-sectional view taken along line I-I of amicro-light-emitting diode device according to a fifth embodiment ofthis disclosure;

FIG. 6 depicts a three-dimensional schematic diagram of amicro-light-emitting diode device according to a sixth embodiment ofthis disclosure;

FIG. 7A to FIG. 7C depict cross-section views of a micro-light-emittingdiode device respectively according to various examples of a sevenembodiment of this disclosure;

FIG. 8A and FIG. 8B depict cross-section views of a micro-light-emittingdiode device respectively according to various examples of an eightembodiment of this disclosure;

FIG. 9A to FIG. 9D depict bottom schematic diagrams of amicro-light-emitting diode device respectively according to variousexamples of a ninth embodiment of this disclosure;

FIG. 10A to FIG. 10L depict schematic diagrams of a method formanufacturing a micro-light-emitting diode device respectively atdifferent steps according to a first embodiment of this disclosure;

FIG. 11A and FIG. 11B depict cross-section views of the first substratein FIG. 10C respectively according to various embodiments; and

FIG. 12A to FIG. 12D depict cross-section views of a method formanufacturing a micro-light-emitting diode device respectively atdifferent steps according to a second embodiment of this disclosure.

DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

Example embodiments will now be described more fully with reference tothe accompanying drawings, in which some example embodiments are shown.Example embodiments, may, however, be embodied in many different formsand should not be construed as being limited to the embodiments setforth herein; rather, these example embodiments are provided so thatthis disclosure will be thorough and complete, and will fully convey thescope of example embodiments of inventive concepts to those of ordinaryskill in the art. In the drawings, the thicknesses of layers and regionsare exaggerated for clarity.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements or layers should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” “on” versus “directly on”). As used herein the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, components, regions,layers and/or sections. These elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of example embodiments.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. Like reference numerals referto like elements throughout. The same reference numbers indicate thesame components throughout the specification.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper”, and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “includes” and/or “including,” if usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

Since micro-light-emitting diode devices are characterized by a smallsize, they have more and wider ranges of applications, such as beingsuitable to be used as pixels of a display, wherein the small size ismicrometers scale size. However, the small size that themicro-light-emitting diode devices have decreases the light-emittingarea, which in turn causes the problem of insufficient light emission.In view of this, the second semiconductor layer of themicro-light-emitting diode device of the present disclosure has multiplethicknesses, in which the thickness at a center area is greater thanedge area, and the center area is surrounded by the edge area.

The minimum thicknesses of the micro-light-emitting diode device islocated at an edge or at least one side. The cross section of thelight-exiting surface thus has a more protruding center. Therefore, theprobability that the light is totally reflected inside themicro-light-emitting diode device is reduced to increase the lightextraction efficiency of the micro-light-emitting diode.

FIG. 1A and FIG. 1B respectively depict a three-dimensional schematicdiagram and a cross-section view of a micro-light-emitting diode device100 according to a first embodiment of this disclosure. Themicro-light-emitting diode device 100 includes a first semiconductorlayer 110, an active layer 120, and a second semiconductor layer 130.The first semiconductor layer 110 has a first bottom surface 112. Theactive layer 120 is disposed on the first semiconductor layer 110. Thesecond semiconductor layer 130 is disposed on the active layer 120 andhas a second bottom surface 132. A surface of the second semiconductorlayer 130 opposite to the active layer 120 is a light-exiting surface140 of the micro-light-emitting diode device 100. Wherein light 104emitted from the active layer to the light-exiting surface 140. Thesecond semiconductor layer 130 has multiple thicknesses. The thicknessrefers to a vertical distance between the second bottom surface 132 andthe light-exiting surface (the surface of the second semiconductorlayer) 140. For example, a first thickness H1 is the thickness at acenter 141 of the second semiconductor layer 130, and a second thicknessH2 is the thickness at an edge (for example end point 142) of the secondsemiconductor layer 130. A minimum thickness of the second semiconductorlayer 130 is located at the edge. That is, the light-exiting surface 140is separated by a distance from an interface between the active layer120 and the second semiconductor layer 130, and the distance decreasesfrom a central axis of the second semiconductor layer 130 to an edge ofthe second semiconductor layer 130. Vertical-projection zones of thefirst semiconductor layer 110, the active layer 120, and the secondsemiconductor layer 130 on the first bottom surface 112 aresubstantially the same.

In FIG. 1A and FIG. 1B, the micro-light-emitting diode device 100 uses atop surface of the second semiconductor layer 130 as the light-exitingsurface 140. The second bottom surface 132 of the second semiconductorlayer 130 is a flat surface. That is, a top surface of the active layer120 is a flat surface. According to the present embodiment, the secondsemiconductor layer 130 has a spherical light-exiting surface 140. Thelight-exiting surface 140 has a first apex 141 and a first end point142. A vertical distance between the first apex 141 and the secondbottom surface 132 is a maximum among the thicknesses of the secondsemiconductor layer 130. A vertical distance between the first end point142 and the second bottom surface 132 is a minimum among the thicknessesof the second semiconductor layer 130. In other words, a position of thefirst apex 141 of the light-exiting surface 140 (or a substantialcenter) is located at a highest point of the light-exiting surface 140,and a tangent of which is parallel with the second bottom surface 132.In addition, the second semiconductor layer 130 depicted in FIG. 1A andFIG. 1B can be regarded as a combination of a pillar (here, the shape ofthe pillar may be cylindrical or polygonal) and part of a sphere. Thepillar is indicated by an arrow 108. The part of the sphere is indicatedby an arrow 106.

Since a previous micro-light-emitting diode device has a flatlight-exiting surface, parts of light emitted from the active layer tothe light-exiting surface will be trap lights in the inside of thesecond semiconductor layer 130. In the present embodiment, by designinga shape of the light-exiting surface 140 that can improve lightextraction effective and reduce light trap in the second semiconductorlayer 130. Hence, a probability that the light 104 emitted from theactive layer 120 is totally reflected off the light-exiting surface 140is reduced to increase a light extraction efficiency of themicro-light-emitting diode device 100. Additionally, the sphericallight-exiting surface 140 also increases a light-exiting surface area ofthe micro-light-emitting diode device 100 to improve overall brightnessof the micro-light-emitting diode device 100. In addition to that, sincethe light-exiting surface 140 is a surface (top surface) of the secondsemiconductor layer, there is no necessity to dispose an additional lensto realize such a configuration.

According to the present embodiment, not only does the sphericallight-exiting surface 140 effectively reduce the probability that thelight 104 is trap inside the micro-light-emitting diode device 100, butthe spherical light-exiting surface 140 also provides a focusing effectfor the light 104. That is, the spherical light-exiting surface 140provides the light 104 with a better directivity. Brightness of themicro-light-emitting diode device 100 is thus improved relatively.

In the present embodiment, P-N heterojunctions in themicro-light-emitting diode device 100 include a junction between theactive layer 120 and the first semiconductor layer 110 and a junctionbetween the active layer 120 and a second semiconductor layer 130. TheP-N heterojunctions can be regarded as light-emitting areas of themicro-light-emitting diode device 100. Since a size of thevertical-projection zones of the first semiconductor layer 110, theactive layer 120, and the second semiconductor layer 130 on the firstbottom surface 112 are substantially the same, a length and a width ofthe P-N heterojunctions in the micro-light-emitting diode device 100 areapproximately the same as a length and a width of the first bottomsurface 112. In other words, the micro-light-emitting diode device 100according to the present embodiment can reduce the probability of totalreflection without changing a size of the P-N heterojunctions. Ingreater detail, the light-emitting areas of the micro light-emittingdiode device 100 will not be reduced, that is, a light extraction amountof the PN heterojunctions is not affected.

The thickness of the second semiconductor layer 130 gradually decreasesfrom the first apex 141 (or the substantial center) to the first endpoint 142 of the light-exiting surface 140. The vertical distancebetween the first apex 141 and the second bottom surface 132 of thesecond semiconductor layer 130 is the first thickness H₁. The verticaldistance between the first end point 142 and the second bottom surface132 of the second semiconductor layer 130 is the second thickness H₂. Asmentioned previously, the first thickness H₁ is the maximum among thethicknesses of the second semiconductor layer 130. The second thicknessH₂ is the minimum among the thicknesses of the second semiconductorlayer 130. With such a thickness relationship in the configuration, thefirst thickness H₁ is more than 0 micrometer (μm) and less than or equalto 20 micrometers, and the second thickness H₂ is more than 0 micrometerand less than or equal to 10 micrometers. Additionally, although thesecond semiconductor layer 130 according to the present embodimentcombining the pillar and the part of the sphere serves as an example forillustration, the micro-light-emitting diode device 100 of the presentdisclosure is not limited in this regard.

In the present embodiment, a size of the micro-light-emitting diodedevice 100 is between 25 square micrometers (μm²) and 10000 squaremicrometers. A side length limitation of the micro-light-emitting diodedevice 100 is less than 100 micrometers (μm). In practices, themicro-light-emitting diode device 100 is used as a pixel of a displaypanel. The size of the micro-light-emitting diode device 100 accordingto the predetermined size of the pixel of the display panel may be anysuitable adjustment.

According to the present embodiment, for example the first semiconductorlayer 110 is a P-type semiconductor. The second semiconductor layer 130is an N-type semiconductor. A thickness of the P-type semiconductor ismore than 0.1 micrometers and less than or equal to 1 micrometer (μm). Athickness of the N-type semiconductor is more than 0.1 micrometers (μm)and less than or equal to 20 micrometers (μm). A thickness of the activelayer 120 is between 0.5 nanometers (nm) and 50 nanometers (nm).

In addition, materials of the P-type semiconductor and the N-typesemiconductor are varied with color light provided by themicro-light-emitting diode device 100. For example, when themicro-light-emitting diode device 100 is designed to provide red light,the P-type semiconductor and the N-type semiconductor may be galliumarsenide (GaAs) or other suitable materials. When themicro-light-emitting diode device 100 is designed to provide blue lightor green light, the P-type semiconductor and the N-type semiconductormay be gallium nitride (GaN), zinc selenide (ZnSe), or aluminum nitride(AlN), or other suitable materials. A material of the active layer 120may be gallium nitride or indium gallium nitride (InGaN), or othersuitable materials.

However, it should be understood that the above-mentioned types ofsemiconductor layers are for illustrative purposes only and are notintended to limit the present invention. Those of ordinary skill in theart may flexibly select types of the first semiconductor layer 110 andthe second semiconductor layer 130 depending on practical needs. Inaddition, those of ordinary skill in the art may additionally dispose aP⁺-type semiconductor layer or an N⁺-type semiconductor layer to improvethe ohmic contact(s) when the micro-light-emitting diode device 100 isconnected to electrodes.

In addition to that, a shape and a size of the first bottom surface 112of the first semiconductor layer 110 are substantially the same as ashape and a size of the second bottom surface 132 of the secondsemiconductor layer 130. As mentioned previously, since a size ofvertical-projection zones of the first semiconductor layer 110, theactive layer 120, and the second semiconductor layer 130 on the firstbottom surface 112 are substantially the same, a shape of themicro-light-emitting diode device 100 as viewed from the top is the sameas that as viewed from the first bottom surface 112 of the firstsemiconductor layer 110.

FIG. 2 depicts a cross-section view of the micro-light-emitting diodedevice 100 according to a second embodiment of this disclosure. Thedifference between the present embodiment and the first embodiment isthat a shape of the second semiconductor layer 130 according to thefirst embodiment is formed by stacking the pillar (here, the shape ofthe pillar may be cylindrical or polygonal) and the part of the sphere(see FIG. 1A), whereas the shape of the second semiconductor layer 130according to the present embodiment is formed by removing the cylinderbut retaining the part of the sphere.

According to the present embodiment, the second semiconductor layer 130has the first thickness H₁ and the second thickness H₂. The firstthickness H₁ is the vertical distance between the center of thelight-exiting surface 140 and the second bottom surface 132, and thefirst thickness H₁ is the maximum among the thicknesses of the secondsemiconductor layer 130. The second thickness H₂ is the thickness of thesecond semiconductor layer 130 corresponding to an edge of thelight-exiting surface 140. That is, the second thickness H₂ is theminimum among the thicknesses of the second semiconductor layer 130, andthe second thickness is approximately 0. In other words, a length of thesecond thickness H₂ and a position of the first end point 142 marked inFIG. 2 are only schematic, and their length and position arecorresponding to the minimum thickness of the second semiconductor layer130.

In addition to that, since the thicknesses and materials of the firstsemiconductor layer 110, the active layer 120, and the secondsemiconductor layer 130 according to the present embodiment are the sameas those according to the first embodiment, a description in this regardis not provided.

FIG. 3A and FIG. 3B respectively depict a three-dimensional schematicdiagram and a cross-section view of the micro-light-emitting diodedevice 100 according to a third embodiment of this disclosure. Thedifference between the present embodiment and the first embodiment isthat the second semiconductor layer 130 according to the presentembodiment is in a pyramidal shape. A shape of the second semiconductorlayer 130 is a pentagon when viewed from a side. The center of thelight-exiting surface 140 is located at an apex of the pyramidal secondsemiconductor layer 130, and the edge of the light-exiting surface 140is aligned with a side of the micro-light-emitting diode device 100. Inthe present embodiment, the apex of the second semiconductor layer 130is the first apex 141. A corner at the edge of the light-exiting surface140 is regarded as the first end point 142. The first apex 141 may bethe center or off the center of the light-exiting surface 140, but thepresent invention is not limited in this regard.

The second semiconductor layer 130 has the first thickness H₁ and thesecond thickness H₂. Similarly, the first thickness H₁ is the verticaldistance between the first apex 141 and the second bottom surface 132,and the first thickness H₁ is the maximum among the thicknesses of thesecond semiconductor layer 130. The second thickness H₂ is the verticaldistance between the first end point 142 and the second bottom surface132, and the second thickness H₂ is the minimum among the thicknesses ofthe second semiconductor layer 130. That is, the minimum thickness ofthe second semiconductor layer 130 is located at at least one side ofthe second semiconductor layer 130. In addition, the thickness of thesecond semiconductor layer 130 linearly decreases from the first apex141 to the first end point 142.

Similarly, the first thickness H₁ is more than 0 micrometer and lessthan or equal to 20 micrometers, and the second thickness H₂ is morethan 0 micrometer and less than or equal to 10 micrometers according tothe present embodiment. In addition, in the present embodiment, adifference between the first thickness H₁ and the second thickness H₂ ismore than 0 micrometer and less than or equal to 10 micrometers.

In addition to that, since the structures and materials of the firstsemiconductor layer 110 and the active layer 120 and the material of thesecond semiconductor layer 130 according to the present embodiment arethe same as those according to the first embodiment, a description inthis regard is not provided.

FIG. 4A and FIG. 4B respectively depict a three-dimensional schematicdiagram and a cross-section view of the micro-light-emitting diodedevice 100 according to a fourth embodiment of this disclosure. Thedifference between the present embodiment and the third embodiment isthat a shape of the second semiconductor layer 130 according to thepresent embodiment is a triangle when viewed from a side, and the secondthickness H₂ of the second semiconductor layer 130 is approximately 0.In addition to that, since the structures and materials of the firstsemiconductor layer 110 and the active layer 120 and the material of thesecond semiconductor layer 130 according to the present embodiment arethe same as those according to the third embodiment, a description inthis regard is not provided. Similarly, the length of the secondthickness H₂ and the position of the first end point 142 marked in FIG.4B are only schematic, and their length and position are correspondingto the minimum thickness of the second semiconductor layer 130.

FIG. 5A and FIG. 5B respectively depict a three-dimensional schematicdiagram and a side cross-sectional schematic diagram taken along lineI-I of the micro-light-emitting diode device 100 according to a fifthembodiment of this disclosure. The difference between the presentembodiment and the first embodiment is that a cross-sectional shape ofthe second semiconductor layer 130 taken along line I-I according to thepresent embodiment is an inverted T-shape. Hence, a cross section of thelight-exiting surface 140 taken along line I-I is an inverted T-shapecorrespondingly.

In greater detail, the inverted T-shaped second semiconductor layer 130has a protruding first area A₁ and a second area A₂ surrounding thefirst area A₁. The second semiconductor layer 130 has the uniform firstthickness H₁ and the uniform second thickness H₂ respectivelycorresponding to the first area A₁ and the second area A₂. The firstthickness H₁ is greater than the second thickness H₂. The secondsemiconductor layer 130 thus has at least one step between the firstarea A₁ and the second area A₂.

Similarly, the first thickness H₁ is more than 0 micrometer and lessthan or equal to 20 micrometers, and the second thickness H₂ is morethan 0 micrometer and less than or equal to 10 micrometers. According tothe present embodiment, a difference between the first thickness H₁ andthe second thickness H₂ of the light-exiting surface 140 is more than 0micrometer and less than or equal to 10 micrometers.

In addition, when light progresses from the first area A₁ towards thesecond area A₂ of the second semiconductor layer 130, an incident angleof part of the light on the light-exiting surface 140 corresponding tothe second area A₂ is relatively larger than an incident angle of thelight on the light-exiting surface 140 corresponding to the first areaA₁. As a result, a probability of total reflection occurring on thelight-exiting surface 140 located in the second area A₂ is higher than aprobability of total reflection on the light-exiting surface 140 locatedin the first area A₁. In the configuration of the present embodiment,part of the light progressing from the first area A₁ towards the secondarea A₂ is exited from a side 134, such as a path of the light 104 shownin FIG. 5B. In other words, the inverted T-shaped light-exiting surface140 can increase the surface area to increase the light extractionprobability of the light 104. Additionally, an incident angle of thelight 104 is changed because of the step 160 to reduce total reflectionso as to reduce the probability that the light 104 is totally reflectedinside the micro-light-emitting diode device 100.

In summary, the second semiconductor layer 130 and the light-exitingsurface 140 of the micro-light-emitting diode device 100 according tothe present embodiment are inverted T-shapes and the secondsemiconductor layer 130 has the step 160 to reduce the probability oftotal reflection and increase the light extraction efficiency.

In addition to that, an area of the light-exiting surface 140corresponding to a position of the second semiconductor layer 130 havingthe first thickness H₁ occupies 65% to 85% of a total area of thelight-exiting surface 140. That is, the light-exiting surface 140located in the first area A₁ occupies 65% to 85% of a total area of thelight-exiting surface 140. Under such a configuration, the probabilityof total reflection occurring inside the micro-light-emitting diodedevice 100 is effectively reduced to further increase the lightextraction efficiency of the micro-light-emitting diode device 100.

However, those of ordinary skill in the art may flexibly select thenumber of the steps 160 depending on practical needs. For example, thelight-exiting surface 140 is designed to be a stepped (a plurality ofsteps 160) surface. Additionally, since the structures and materials ofthe first semiconductor layer 110 and the active layer 120 and thematerial of the second semiconductor layer 130 according to the presentembodiment are the same as those according to the first embodiment, adescription in this regard is not provided.

FIG. 6 depicts a three-dimensional schematic diagram of amicro-light-emitting diode device according to a sixth embodiment ofthis disclosure. The difference between the present embodiment and thefifth embodiment is that the second areas A₂ of the second semiconductorlayer 130 according to the present embodiment are located on twoopposites of the first area A₁. The cross section of the secondsemiconductor layer 130 is an inverted T-shape and the secondsemiconductor layer 130 has the protruding first area A₁. Portionslocated on the two opposite sides of the first area A₁ are the secondareas A₂ of the second semiconductor layer 130.

Similarly, the minimum thickness of the second semiconductor layer 130is located at least one side of the second semiconductor layer 130. Thefirst area A₁ and the second areas A₂ of the second semiconductor layer130 respectively have the first thickness H₁ and the second thicknessH₂. The first thickness H₁ is greater than the second thickness H₂. Thesecond semiconductor layer 130 thus has the step 160 between the firstarea A₁ and each of the second areas A₂. Since the configuration of thefirst thickness H₁ and the second thickness H₂ of the secondsemiconductor later 130 is the same as that of the fifth embodiment, adescription in this regard is not provided. In addition, an area of thelight-exiting surface 140 located in the first area A₁ similarlyoccupies 65% to 85% of the total area of the light-exiting surface 140.

In addition to that, since the structures of the first semiconductorlayer 110 and the active layer 120 according to the present embodimentare the same as those according to the first embodiment, and thematerials of the first semiconductor layer 110, the active layer 120,and the second semiconductor layer 130 are also the same as those of thefirst embodiment, a description in this regard is not provided.

FIG. 7A to FIG. 7C depict cross-section views of themicro-light-emitting diode device 100 respectively according to variousexamples of a seven embodiment of this disclosure. The light-exitingsurface 140 of the micro-light-emitting diode device 100 according tothe present embodiment has at least one microstructure 150. In FIG. 7Aand FIG. 7B, the light-exiting surfaces 140 of the micro-light-emittingdiode device 100 according to the first embodiment having themicrostructures 150 are taken for example. In FIG. 7C, the light-exitingsurface 140 of the micro-light-emitting diode device 100 according tothe fifth embodiment having the microstructure 150 is taken for example.

In the present embodiment, the microstructure 150 includes a recessedportion or a raised portion. For example, the microstructures 150 inFIG. 7A and FIG. 7C include the raised portions. The raised portionsserve as protruding structures of a surface of the second semiconductorlayer 130. The microstructure 150 in FIG. 7B includes the recessedportions. The recessed portions serve as recessed structures (that is,the dashed line depicted in FIG. 7B represents positions of the recessedstructures that the surface of the second semiconductor layer 130 has)of the surface of the second semiconductor layer 130. By utilizing themicrostructure 150, an incident angle of light emitted from the activelayer 120 to the light-exiting surface 140, and incident angle of lighton the light-exiting surface 140 is changed again to reduce theprobability that the light is totally reflected inside themicro-light-emitting diode device 100 the second time. As a result, thelight extraction efficiency of the micro-light-emitting diode device 100is increased.

In addition to that, since the structures and materials of the firstsemiconductor layer 110, the active layer 120, and the secondsemiconductor layer 130 according to the present embodiment are the sameas those of the embodiments corresponding to the present embodiment, adescription in this regard is not provided.

FIG. 8A and FIG. 8B depict cross-section views of themicro-light-emitting diode device 100 respectively according to variousexamples of an eight embodiment of this disclosure. Themicro-light-emitting diode device 100 according to the presentembodiment further includes an electrode layer 170. In FIG. 8A, theelectrode layer 170 being disposed on the micro-light-emitting diodedevice 100 according to the first embodiment is taken for example. InFIG. 8B, the electrode layer 170 being disposed on themicro-light-emitting diode device 100 according to the fifth embodimentis taken for example.

In the present embodiment, the electrode layer 170 is disposed on thesecond semiconductor layer 130. The electrode layer 170 has a uniformthickness, and a shape of the electrode layer 170 corresponds to theshape of the light-exiting surface 140. For example, the electrodelayers 170 in FIG. 8A and FIG. 8B are respectively in a spherical shapeand in an inverted-T shape. Since the shape of the electrode layer 170corresponds to the shape of the light-exiting surface 140, theprobability that light is totally reflected inside themicro-light-emitting diode device 100 still can be maintained relativelylow.

A material of the electrode layer 170 is a transparent electrodematerial, such as indium-gallium-zinc oxide (IGZO), indium-tin oxide(ITO), indium-zinc oxide (IZO), zinc-tin oxide (ZTO), gallium-zinc oxide(GZO), or other suitable materials, or combinations thereof.

In addition to that, since the structures and materials of the firstsemiconductor layer 110, the active layer 120, and the secondsemiconductor layer 130 according to the present embodiment are the sameas those of the embodiments corresponding to the present embodiment, adescription in this regard is not provided.

FIG. 9A to FIG. 9D depict bottom schematic diagrams of themicro-light-emitting diode device 100 respectively according to variousexamples of a ninth embodiment of this disclosure. As shown in FIG. 9A,the shape of the micro-light-emitting diode device 100 may be arectangle when viewed from the first bottom surface 112. As shown inFIG. 9B, the shape of the micro-light-emitting diode device 100 may be acircle when viewed from the first bottom surface 112. Various polygonalshapes should be within the scope of present embodiment. As shown inFIG. 9C, the shape of the micro-light-emitting diode device 100 may be arectangle when viewed from the first bottom surface 112. As shown inFIG. 9D, the shape of the micro-light-emitting diode device 100 may be atriangle when viewed from the first bottom surface 112.

FIG. 10A to FIG. 10L depict schematic diagrams of a method formanufacturing a micro-light-emitting diode device respectively atdifferent stages according to a first embodiment of this disclosure. Inthe present embodiment, the method for manufacturing themicro-light-emitting diode device is illustrated by taking the structureof the micro-light-emitting diode device according to the firstembodiment (see FIG. 1A) as an example. In addition, FIG. 10A to FIG.10H are cross-section views, and FIG. 10I to FIG. 10L arethree-dimensional schematic diagrams.

As shown in FIG. 10A, in step S10, a first substrate 240 is provided anda mask layer 242 is formed on the first substrate 240. The mask layer242 is formed on the first substrate 240 by deposition. According to thepresent embodiment, the mask layer 242 may be regarded as a hard maskused in an etching process. The mask layer 242 may be made of siliconoxide or silicon nitride.

In addition, selection of material of the first substrate 240 is variedwith color light provided by the micro-light-emitting diode device. Forexample, when a micro-light-emitting diode device providing red light isformed, the first substrate 240 may be made of gallium arsenide (GaAs),gallium phosphide (GaP), indium phosphide (InP), or silicon (Si), orother suitable materials. When a micro-light-emitting diode deviceproviding blue or green light is formed, the first substrate 240 may bemade of sapphire, gallium nitride (GaN), or silicon carbide (SiC), orother suitable materials. In addition, a thickness of the firstsubstrate 240 made of sapphire is between 50 micrometers and 1000micrometers.

As shown in FIG. 10B, in step S20, the mask layer 242 is patterned toexpose a portion of the first substrate 240. The patterned mask layer242 and the exposed first substrate 240 can be used for defining a sizeof the micro-light-emitting diode device.

As shown in FIG. 10C, in step S30, the portion of the first substrate240 are etched to form a recess 244. The first substrate 240 has a firstshape corresponding to the recess 244. The portions of the firstsubstrate 240 may be etched by, for example, photolithography andetching.

A description is provided with reference to FIG. 1A, FIG. 1B, and FIG.10C. The recess 244 is used for depositing the second semiconductorlayer 130 of the micro-light-emitting diode device 100. The secondsemiconductor layer 130 has the light-exiting surface 140, and thelight-exiting surface 140 has a second shape. The first shape of thefirst substrate 240 is the same as the second shape of the light-exitingsurface 140. In greater detail, the shape of the light-exiting surface140 is the same as a shape of the recess 244 of the first substrate 240.For example, the shape of the light-exiting surface 140 and the shape ofthe recess 244 of the first substrate 240 are both spheres.

Additionally, the recess 244 has a first depth D₁ and a second depth D₂corresponding to the light-exiting surface 140. The first depth D₁ isgreater than the second depth D₂. The first depth D₁ is a depth at acenter of the recess 244, and the first depth D₁ is a maximum amongdepths of the recess 244. The second depth D₂ is an initial depth of therecess 244 corresponding to an edge. That is, the second depth D₂ is aminimum among the depths of the recess 244.

As shown in FIG. 10D, in step S40, the mask layer 242 (see FIG. 10C) isremoved and the first substrate 240 having the recess 244 is left. Themask layer 242 is removed by etching according to the presentembodiment.

As shown in FIG. 10E, in step S50, the second semiconductor layer 130 isfirst deposited on the recess 244 of the first substrate 240. A surfaceof the second semiconductor layer 130 contacting the recess 244 formsthe second shape, and the second shape is the same as the first shape ofthe first substrate 240.

Then, metal organic chemical-vapor deposition (MOCVD) is utilized todeposit the active layer 120 and the first semiconductor layer 110 insequence. The active layer 120 is deposited on the second semiconductorlayer 130. The first semiconductor layer 110 is deposited on the activelayer 120 to complete formation of the micro-light-emitting diode device100 on the first substrate 240.

In the present embodiment, the micro-light-emitting diode device 100includes the first semiconductor layer 110, the active layer 120, andthe second semiconductor layer 130. Since the thicknesses and materialsof the first semiconductor layer 110, the active layer 120, and thesecond semiconductor layer 130 are the same as those of themicro-light-emitting diode device 100 according to the first embodiment,a description in this regard is not provided.

As shown in FIG. 10F, in step S60, the first substrate 240 and themicro-light-emitting diode device 100 are transferred and reversed to asecond substrate 246. The first semiconductor layer 110 of themicro-light-emitting diode device 100 is connected to the secondsubstrate 246. That is, the micro-light-emitting diode device 100 islocated between the first substrate 240 and the second substrate 246.Additionally, the second substrate 246 may be a glass substrate, aplastic substrate, or a flexible substrate.

As shown in FIG. 10G, in step S70, the first substrate 240 is removed toallow the first substrate 240 (see FIG. 10F) to be separated from themicro-light-emitting diode device 100. In addition to that, the step ofremoving the first substrate 240 may be performed by the laser lift-offtechnology. After the first substrate 240 is removed 240, thelight-exiting surface 140 of the second semiconductor layer 130 isexposed to complete the structure of the micro-light-emitting diodedevice 100.

As shown in FIG. 10H, in step S80, the size of the micro-light-emittingdiode device 100 is further defined. According to the presentembodiment, the size of the micro-light-emitting diode device 100 may bedefined by etching. Etching first semiconductor layer 110 {grave over ()} active layer 120 and second semiconductor layer 130 in the same timeto define a size of a micro-light-emitting diode device. For example, aphotoresist layer 248 is coated and a lithography process is utilized todefine the size of the micro-light-emitting diode device 100. Afterdefining the size of the micro-light-emitting diode device 100, thephotoresist layer 248 is removed. Vertical-projection zones of the firstsemiconductor layer 110, the active layer 120, and the secondsemiconductor layer 130 thus etched on the first bottom surface 112 ofthe first semiconductor layer 110 are substantially the same.

As shown in FIG. 10I, in step S90, a panel 250 comprises a plurality ofpixels (not show in figure). Each of the plurality of pixels is providedat least one thin film transistor 252. The thin film transistor 252 isused for connecting to the corresponding micro-light-emitting diodedevice 100 thus manufactured the panel 250. (see FIGS. 10I to 10L).However, those of ordinary skill in the art may flexibly arrange thethin film transistors 252 and the micro-light-emitting diode device 100relationship.

As shown in FIG. 10J, in step S100, the micro-light-emitting diodedevice 100 thus manufactured is gripped to allow themicro-light-emitting diode device 100 to be separated from the secondsubstrate 246 along the arrow direction. According to the presentembodiment, the step of separating the micro-light-emitting diode device100 from the second substrate 246 is performed by a transposition means254.

As shown in FIG. 10K, in step S110, the micro-light-emitting diodedevice 100 is moved onto the thin film transistor 252 on the panel 250by the transposition means 254 to allow the micro-light-emitting diodedevices 100 to be combined with the thin film transistor 252 on thepanel 250. According to the present embodiment, a pixel configuration ofthe pixel 250 can be completed by performing step S110 repeatedly.

Then, a description is provided with reference to FIG. 10L. As shown inFIG. 10L, in step S120, the electrode layers 170 are disposed on thesecond semiconductor layers 130 of the micro-light-emitting diodedevices 100 to complete a display panel utilizing themicro-light-emitting diode device 100.

Although the structure of the micro-light-emitting diode device 100according to the first embodiment being manufactured in FIG. 10A to FIG.10L is taken for example, those of ordinary skill in the art may etchthe substrate 240 into different first shapes by photolithography toallow the first shape of the first substrate 240 to correspond to thelight-exiting surface 140 in different shapes.

For example, a description is provided with reference to FIG. 11A andFIG. 11B. FIG. 11A and FIG. 11B depict cross-section views of the firstsubstrate 240 in FIG. 10C respectively according to various embodiments.In FIG. 11A, the first substrate 240 can be etched into the first shapethat is an inverted triangle so as to correspond to the shapes of thelight-exiting surfaces 140 of the micro-light-emitting diode devices 100in the third embodiment and the fourth embodiment. In FIG. 11B, thefirst substrate 240 can be etched into the first shape that has a stepso as to correspond to the shapes of the light-exiting surfaces 140 ofthe micro-light-emitting diode devices 100 in the fifth embodiment andthe sixth embodiment.

FIG. 12A to FIG. 12D depict cross-section views of a method formanufacturing a micro-light-emitting diode device respectively atdifferent stages according to a second embodiment of this disclosure.The difference between the present embodiment and the previousembodiment is that the second semiconductor layer 130 according to thepresent embodiment fills and levels up the recess 244 by deposition.That is, the second semiconductor layer 130 fills up only in the recess244 and the second semiconductor layer 130 does not overflow the recess244. In addition to that, a structure of the micro-light-emitting diodedevice 100 formed according to the present embodiment is the same asthat of the micro-light-emitting diode device according to the secondembodiment (see FIG. 2).

First, a description is provided with reference to FIG. 12A. FIG. 12Adepicts a process following FIG. 10D. As shown in FIG. 12A, in stepS50′, the second semiconductor layer 130 is only deposited in the recess244. That is, the second bottom surface 132 of the second semiconductorlayer 130 and a top surface of the first substrate 240 are coplanar.Similarly, the active layer 120 is deposited on the second semiconductorlayer 130. The first semiconductor layer 110 is deposited on the activelayer 120 to complete the formation of the micro-light-emitting diodedevice 100 on the first substrate 240.

As shown in FIG. 12B, in step S60′, the first substrate 240 and themicro-light-emitting diode device 100 are transferred to a secondsubstrate 246. The micro-light-emitting diode device 100 is locatedbetween the first substrate 240 and the second substrate 246.

As shown in FIG. 12C, in step S70′, the first substrate 240 can beremoved by a manufacturer at this time to expose the light-exitingsurface 140 and part of the active layer 120 of the micro-light-emittingdiode device 100.

As shown in FIG. 12D, in step S80′, the size of the micro-light-emittingdiode device 100 is further defined by etching. According to the presentembodiment, the part of the active layer 120 that is exposed and part ofthe first semiconductor layer 110 underneath the part of the activelayer 120 that is exposed are removed by etching. Hence,vertical-projection zones of the first semiconductor layer 110 and theactive layer 120 thus etched and the second semiconductor layer 130 onthe first bottom surface 112 of the first semiconductor layer 110 aresubstantially the same.

In summary, since the second semiconductor layer of themicro-light-emitting diode device of the present disclosure has agreater thickness at the center than at the edge, the cross section ofthe light-exiting surface has a more protruding center. Therefore, theprobability that the light is totally reflected inside themicro-light-emitting diode device is reduced to increase the lightextraction efficiency of the micro-light-emitting diode.

Although the present disclosure has been described in considerabledetail with reference to certain embodiments thereof, other embodimentsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the embodiments containedherein.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentdisclosure without departing from the scope or spirit of the disclosure.In view of the foregoing, it is intended that the present disclosurecover modifications and variations of the present disclosure providedthey fall within the scope of the following claims.

What is claimed is:
 1. A micro-light-emitting diode device comprising: afirst semiconductor layer having a first bottom surface; an active layerdisposed on the first semiconductor layer; and a second semiconductorlayer disposed on the active layer, wherein the second semiconductorlayer and the active layer have an interface, a surface of the secondsemiconductor layer opposite to the active layer is a light-exitingsurface of the micro-light-emitting diode device, a distance between thelight-exiting surface and the interface decreases from a central axis ofthe second semiconductor layer to an edge of the second semiconductorlayer, and a light pass through the light-exiting surface of themicro-light-emitting diode device configured to redirect or focus thelight that would otherwise be trapped or absorbed in themicro-light-emitting diode device, and vertical-projection zones of thefirst semiconductor layer, the active layer, and the secondsemiconductor layer on the first bottom surface are substantially thesame.
 2. The micro-light-emitting diode device of claim 1, wherein thelight-exiting surface has a first apex and a first end point, a verticaldistance between the first apex and the second bottom surface is amaximum among the thicknesses of the second semiconductor layer, and avertical distance between the first end point and the second bottomsurface is a minimum among the thicknesses of the second semiconductorlayer.
 3. The micro-light-emitting diode device of claim 2, wherein avertical distance between the light-exiting surface and the secondbottom surface gradually decreases from the first apex to the first endpoint.
 4. The micro-light-emitting diode device of claim 3, wherein thelight-exiting surface is in one of a spherical shape, an inverted-Tshape, and a pointed shape.
 5. The micro-light-emitting diode device ofclaim 4, wherein a shape of the first bottom surface of the firstsemiconductor layer is a circle or a polygon, and the shape and a sizeof the first bottom surface are substantially the same as a shape and asize of the second bottom surface.
 6. The micro-light-emitting diodedevice of claim 2, wherein the vertical distance between the first apexand the second bottom surface is more than 0 micrometer and less than orequal to 20 micrometers.
 7. The micro-light-emitting diode device ofclaim 2, wherein the vertical distance between the first end point andthe second bottom surface is more than 0 micrometer and less than orequal to 10 micrometers.
 8. The micro-light-emitting diode device ofclaim 2, wherein a difference between the vertical distance between thefirst apex and the second bottom surface and the vertical distancebetween the first end point and the second bottom surface is more than 0micrometer and less than or equal to 10 micrometers.
 9. Themicro-light-emitting diode device of claim 1, wherein the light-exitingsurface has at least one microstructure, the microstructure comprises aplurality of recessed portions or a plurality of raised portions. 10.The micro-light-emitting diode device of claim 1, wherein the secondsemiconductor layer has a first thickness corresponding to a first area,the second semiconductor layer has a second thickness corresponding to asecond area, the first thickness is greater than the second thicknesssuch that the second semiconductor layer has at least one step betweenthe first area and the second area.
 11. The micro-light-emitting diodedevice of claim 10, wherein an area corresponding to the first thicknessof the second semiconductor layer occupies 65% to 85% of a total area ofthe light-exiting surface.
 12. The micro-light-emitting diode device ofclaim 10, wherein the second area surrounds the first area.
 13. Themicro-light-emitting diode device of claim 1, further comprising anelectrode layer disposed on the second semiconductor layer.
 14. Themicro-light-emitting diode device of claim 13, wherein a shape of theelectrode layer corresponds to a shape of the light-exiting surface.